Suspension problem
2001 Cadillac SLS V8 Front Wheel Drive Automatic 140000 miles

Hi, 01 cadillac SLS. The back of my car is lifted all the way into the air, making my car look like a drag racer. I was told it could be one of two things, either the compressors' exhaust is not working or the height sensor. I have purchased a new compressor but dont want to remove my stock compressor if the height sensor is the problem. The compressor runs for about 5 seconds after I first start the vehicle, and then it never comes on again but the car stays jacked up. Is there a way of knowing which component is really not working? I have run the DTC codes for the vehicle and I have none. I was also told to put 300 hundered pounds into the trunk after starting the car and letting the pump cycle so I did and the car stayed up in the rear. The pump never came on nor did it exhaust so does this mean my height sensor is bad or the exhaust in the compressor just isnt working? Please help. Thanks in advance